Recently, a white light-emitting device (LED), which is getting the lime light as a lighting, an LED backlight, a lighting lamp for vehicle or the like, generally includes a light-emitting element emitting a blue or a near infrared ray, and a phosphor converting a wavelength into a visible ray by using, as an excitation source, light emitted from the light-emitting element.
In a typical method for realizing the white LED, a blue light-emitting element formed of an InGaN-based material having a wavelength of 450-550 nm, is used as a light-emitting element, and a YAG-based phosphor that is expressed by an empirical formula of (Y,Gd)3(Al,Ga)5O12 and emits a yellow, is used. In the white LED, blue light emitted from the light-emitting element, is incident to a phosphor layer, and the incident blue light is absorbed and scattered several times in the phosphor. At this time, the blue light absorbed in the phosphor is changed in wavelength to be converted into yellow light, the yellow light and a portion of the incident blue light are mixed with each other, and thus the mixed color is visible to human eyes as a white
However, the white LED having the aforementioned structure has limitations in that light is low in red component, color temperature is high, and red and green components are insufficient, so only illumination light having a low degraded color rendering property, is obtained.
Also, since an oxide-based phosphor generally shows a tendency that when a wavelength of an excitation source decreases to 400 nm, a light-emitting intensity is reduced, the oxide-based phosphor has a limitation in that high brightness white light is unobtainable by using blue light.
Therefore, an oxynitride-based phosphor, which has stability equal to or more than that of an oxide-based phosphor, and also has excellent light-emitting efficiency even in an excitation source having a wavelength of more than 450 nm, is receiving attention from a white LED field. Also, since the oxynitride-based phosphor is a material that has been originally developed from engineering ceramic, the oxynitride-based phosphor has advantages in that an efficiency reduction and a color conversion due to humidity and heat are low.
However, it is little studied or known about existence of the oxynitride-based phosphor in a composition region deviated from α-type or β-type SiAlON (Si—Al—O—N).